Foamed synthetic polymer cordage



United States Patent ()fiice 3,353,346 Patented Nov. 21, 1967 3,353,346 FGAMED SYNTHETIQ PGLYMER CORDAGE Remo .l. Laureti, Beverly, NJL, assignor to Wail industries, lnc., a corporation of Delaware No Drawing. Filed Get. 23, 1965, Ser. No. 504,149 5 Claims. (63!. 5714t)) This invention relates to foamed synthetic polymer cordage, and a method for making that cordage. In one aspect it relates to the formation of improved synthetic polymer cordage by the use of foamed polymeric fila' ments. In another aspect, it relates to the production of an improved cordage by means of a construction made practical by the use of foamed filaments. In another aspect, it relates to a method of making a cordage of foamed synthetic filaments by twisting the filaments in one direction to make a yarn, twisting several yarns together in an opposite direction to make a strand, and twisting several strands together in the direction of the yarn twist.

Prior to World War II, virtually all rope was manufactured of fibers from hemp. Typically, these ropes were composed of individual combed fibers which were spun into single yarns of one twist direction. For example, yarns could be twisted in the right-hand or Z direction. These yarns were then combined and geometrically placed in concentric layers to form a strand with a twist direction opposite that of the yarns, for example, given a left-hand, or S direction twist. These strands, usually three, but sometimes four, were then twisted together in a direction opposite that of the strand twist, that is, in the Z direction, to form a standard or regular lay rope. Conversely, the fibers might be spun into single yarns having an S twist direction, the yarns then twisted together into Z direction to form a strand, and three or four strands twisted together in the S direction to form the rope.

As various polymeric materials became available, it was recognized that ropes made of these materials would be superior to ropes of natural fibers, especially in strength, durability, and resistance to rotting or chemical attack. Virtually all polymeric materials capable of forming filaments have been woven into ropes, most notably, nylon, polyesters, polyolefins, and polyurethanes.

Attempts to form cordage from these synthetic materials by'using the same twisting techniques as had been used with the natural fibers, however, were unsatisfactory. The elasticity and lastic memory of these materials caused the individual filaments to attempt to return to their original configuration, resulting in a rope susceptible to hockling and untwisting.

Various attempts have been made to overcome these problems. One commonly used method is to form the rope as described above, and then to heat the rope to the softening point of the polymer, and stretch the rope while it is hot. This process, however, requires the extra heat-stretch processing operation during rope manufacturing.

The most satisfactory previous method of making cordage of synthetic filaments, however, involves the use of dilferent types of cordage construction. One of the best of these is known as a plied yarn construction. In this type of construction, the filaments are twisted together in one direction, for example, in an S direction, to form a component yarn. Three of these component yarns are twisted together in a Z direction to form 2. ply yarn. Next, a predetermined number of plied yarns are geometrically placed in concentric layers and twisted together in an S direction to form a strand. Lastly, three strands are twisted in a Z direction to form a rope. Thus, this method of construction required one extra twist operation beyond what had been required for forming a natural fiber rope. A method for forming cordage from synthetic polymers as economically as from natural fibers has long been desired, but heretofore hasbeen unavailable.

It is therefore an object of this invention to provide synthetic cordage using the same twisting techniques suitable for natural fiber cordage. It is a further object of this invention to provide an inexpensive synthetic polymer rope. It is a further object of this invention to provide a synthetic polymer cordage with improved strength to weight ratio. It is a still further object of this invention to provide a rope with increased buoyancy. It is yet a further object of this invention to provide a rope with reduced stretch and snap-back. It is still a further object of this invention to provide a synthetic cordage with reduced tendency toward hockling and untwisting. It is yet a further object of this invention to provide a synthetic rope which has less elasticity and less plastic memory than those heretofore produced.

These and other objects are accomplished by my discovery that a stronger and much improved synthetic polymer cordage can be produced by using foamed synthetic polymer filaments and constructing the cordage with the conventional hemp rope construction technique of twisting the filaments together in one direction to form a yarn, twisting several yarns together in a direction opposite that of the yarn twist to form a strand, and twisting several strands together in a direction opposite that of the strand twist to form the cordage. This method produces a cordage comprising a plurality of strands twisted together in one direction, each of said strands comprising a plurality of yarns twisted together in an opposite direction from the twist of said cordage, each of said yarns comprising a plurality of foamed synthetic filaments twisted together in an opposite direction from the direction of twist of said strand.

Foamed filaments have a less elasticity and plastic memory than unfoamed filaments of the same polymers, and consequently have less tendency to hockle and untwist when formed into cordage. The change of properties obtained by foaming the filaments is sufiicient to allow synthetic foamed filaments to be twisted into ropes using the same twisting techniques as those which were suitable for natural fibers, but which heretofore have been inapplicable to synthetic fibers without special subsequent treatment of the formed rope.

My invention is suitably used with any polymer which may be formed into a filament by extrusion or otherwise. Nylon, polyurethane, and polyolefins are some specific examples of polymers currently used in cordage which are suitable for use with my invention, but my invention is not limited to these polymers. Polymers of aliphatic mono-l-olefins, such as ethylene, propylene, butene-l, hexane-1, octene-l, and the like make particularly desirable cordage. Homopolymers and copolymers of both ethylene and propylene are suitable. It is also within the scope of my invention to use filaments of different polymers in the same cordage, as for example twisting together filaments of propylene and nylon to form a mixed yarn.

Foaming of the thermoplastic filaments generally takes place at extrusion by incorporation of a gas-forming agent in the molten polymer mix, and the subsequent expansion of this gas during the extrusion process. Other techniques suitable for introducing gas bubbles into filaments could be used as well, however. Gas bubbles could be whipped into the viscous plastic, for example, or a leachable solid could be incorporated into the polymer. Polyurethane filaments may be foamed by reaction of their isocyanate groups with water during the cross-linking reaction, as is well known in the art.

If desired, the filaments to be used in the cordage of my invention may be oriented, and usually will be. In general, this orientation can take place prior to twisting the filaments into yarn, but if desired, orientation can take place by stretching the yarn, the strand, or the finished rope.

A filament which has been found particularly suitable for use with my invention is a foamed and oriented polyolefin disclosed in copending application of Bottomley, S.N. 283,950, filed May 21, 1963, now Patent No. 3,214,234.

The amount of foaming necessary to produce satisfactory cordage according to the process of my invention will vary with the type of polymer, the denier of the filaments, tightness of twist of the yarns, the strands and the finished cordage. In general, a filament having approximately 15 to 50 percent void space will be suitable for most applications. This void space serves to make my rope more buoyant than rope of unfoamed filaments.

The ropes of my invention have an improved translation efficiency over unfoamed synthetic ropes of different construction, such as the plied yarn construction described above. Since there is abrasion during the twisting process and strain is introduced into the filaments by twisting, the twisted rope is never as strong as the mathematical sum of the strengths of the individual filaments making up the rope. The ratio of the strength of the rope after twisting to the strength of the components before twisting is known as the translation efficiency. Since there is one less twisting operation in the rope of my invention than in the. plied yarn construction, the translation efliciency of my rope is higher. This results in the rope of my invention having a higher strength to weight ratio than rope of the plied yarn construction. The foamed rope of my invention is therefore less expensive than an unfoamed synthetic rope of the same strength, not only because of the greater strength to weight ratio, but also because my rope has one less twisting operation and therefore is less expensive to manufacture.

Because the foamed filaments have less elasticity and less plastic memory than comparable unfoamed filaments, the cordage produced from these filaments will have reduced stretch and resultant tendency to snap-back, as well as having reduced tendency to hockle or untwist.

It is within the scope of my invention to use filaments which have been subjected to various treatments as are known in the textile art such as dyeing, coating, lubricating, crimping, twisting, false twisting, or any other treatment to modify the characteristics of the filaments. The currently preferred embodiment, however, uses untreated filaments.

Example Filaments of polypropylene containing 0.2 percent by weight of azodicarbonamid were extruded through 40 mil die holes. After foaming, the filaments were oriented by drawing at an 8 to 1 draw ratio. The diameter of filaments after drawing was 14 mils.

Forty of the filaments so formed were twisted together in a Z twist of 12 turns per foot to form a yarn. Twelve of these yarns were twisted together in an direction to form strands having 6.6 turns per foot, and three of the strands so formed were twisted (laid) together in a Z direction to form a rope of 4.5 twists per foot.

The diameter of the rope thus formed was inch diameter, and it weighed 8.50 pounds per 100 feet.

For comparison, a inch diameter rope Was formed of unfoamed polypropylene filaments of 12 mil diameter using the plied yarn construction. Nineteen of these Breaking Weight; Strength/ Load, Percent of Rope, Weight Pounds Elongation Pounds/ Ratio 100 Feet Foamod rope 8, 000 22 8. 94, 000 Control rope 7, 800 40 10. 50 74, 000

It is thus seen that the strength to weight ratio of the rope of my invention is greater than that of currently produced ropes. The elongation at rupture, and the resultant snap-back, is less than currently produced ropes.

Reasonable variation and modification are permissible within the scope of my invention, the essence of which is that a rope may be formed of foamed synthetic polymeric filaments by twisting the filaments together in one direction to form a yarn, twisting a plurality of yarn together in a direction opposite the twist of the yarn to form strands, and twisting said strands together in a direction opposite the direction of twist of said strands to form the cordage.

I claim:

1. Cordage of a foamed synthetic polymer comprising a plurality of strands twisted together in one direction, each of said strands comprising a plurality of yarns twisted together in an opposite direction from the twist of said cordage, each of said yarns comprising a plurality of foamed synthetic filaments twisted together in an opposite direction from the direction of twist ofsaid strand.

2. The cordage of claim 1 wherein said foamed synthetic polymer is nylon.

3. The cordage of claim 1 wherein said foamed synthetic polymer is a polyolefin.

4. The cordage of claim 1 wherein said cordage is a rope, and said foamed synthetic polymer is selected from homopolymers and copolymers of ethylene and homopolymers and copolymers of propylene.

5. The cordage of claim 1 wherein said filaments are oriented prior to twisting into said yarns.

References Cited UNITED STATES PATENTS 2,256,483 9/1941 Johnston.

2,805,465 9/1957 Miller 57-140 X 3,001,359 9/1961 Simon 57-163 X 3,015,150 1/1962 Terni.

3,048,963 8/1962 Himmelfarb et al. 57-157 X 3,092,955 6/1963 Smit 57-157 X 3,118,161 1/1964 Cramton.

3,129,631 4/1964 Hill et al. 57163 X 3,315,454 4/1967 Carranza 57140 FRANK I. COHEN, Primary Examiner. z)

D. WATKINS, Assistant Examiner, 

1. CORDAGE OF A FOAMED SYNTHETIC POLYMER COMPRISING A PLURALITY OF STRANDS TWISTED TOGETHER IN ONE DIRECTION, EACH OF SAID STRANDS COMPRISING A PLURALITY OF YARNS TWISTED TOGETHER IN AN OPPOSITE DIRECTION FROM THE TWIST OF SAID CORDAGE, EACH OF SAID YARNS COMPRISING A PLURALITY OF FOAMED SYNTHETIC FILAMENTS TWISTED TOGETHER IN AN OPPOSITE DIRECTION FROM THE DIRECTION OF TWIST OF SAID STRAND. 